The invention relates to semiconductor processing equipment and more particularly to improved process drift control during processing such as plasma etching of semiconductor substrates.
In the field of semiconductor processing, vacuum processing chambers are generally used for etching and chemical vapor deposition (CVD) of materials on substrates by supplying an etching or deposition gas to the vacuum chamber and application of an RF field to the gas to energize the gas into a plasma state. Examples of parallel plate, transformer coupled plasma (TCP(trademark)) which is also called inductively coupled plasma (ICP), and electron-cyclotron resonance (ECR) reactors and components thereof are disclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; 5,200,232 and 5,820,723. Because of the corrosive nature of the plasma environment in such reactors and the requirement for minimizing particle and/or heavy metal contamination, it is highly desirable for the components of such equipment to exhibit high corrosion resistance.
During processing of semiconductor substrates, the substrates are typically held in place within the vacuum chamber on substrate holders by mechanical clamps and electrostatic clamps (ESC). Examples of such clamping systems and components thereof can be found in commonly owned U.S. Pat. Nos. 5,262,029 and 5,838,529. Process gas can be supplied to the chamber in various ways such as by gas nozzles, gas rings, gas distribution plates, etc. An example of a temperature controlled gas distribution plate for an inductively coupled plasma reactor and components thereof can be found in commonly owned U.S. Pat. No. 5,863,376.
Aluminum and aluminum alloys are commonly used for walls of plasma reactors. In order to prevent corrosion of the walls, various techniques have been proposed for coating the aluminum surface with various coatings. For instance, U.S. Pat. No. 5,641,375 discloses that aluminum chamber walls have been anodized to reduce plasma erosion and wear of the walls. The ""375 patent states that eventually the anodized layer is sputtered or etched off and the chamber must be replaced. U.S. Pat. No. 5,680,013 states that a technique for flame spraying Al2O3 on metal surfaces of an etching chamber is disclosed in U.S. Pat. No. 4,491,496. The ""013 patent states that the differences in thermal expansion coefficients between aluminum and ceramic coatings such as aluminum oxide leads to cracking of the coatings due to thermal cycling and eventual failure of the coatings in corrosive environments. U.S. Pat. No. 5,085,727 discloses a carbon coating for walls of a plasma chamber wherein the coating is deposited by plasma assisted CVD.
In order to protect the chamber walls, U.S. Pat. Nos. 5,366,585; 5,556,501; 5,788,799; 5,798,016; and 5,885,356 propose liner arrangements. For instance, the ""585 patent discloses a free standing ceramic liner having a thickness of at least 0.005 inches and machined from solid alumina. The ""585 patent also mentions use of ceramic layers which are deposited without consuming the underlying aluminum can be provided by flame sprayed or plasma sprayed aluminum oxide. The ""501 patent discloses a process-compatible liner of polymer or quartz or ceramic. The ""799 patent discloses a temperature controlled ceramic liner having a resistance heater embedded therein and the ceramic can be alumina, silica, titania, zirconia, silicon carbide, titanium carbide, zirconium carbide, aluminum nitride, boron nitride, silicon nitride and titanium nitride. The ""016 patent discloses a liner of ceramics, aluminum, steel and/or quartz with aluminum being preferred for its ease of machinability and having a coating of aluminum oxide, Sc2O3 or Y2O3, with Al2O3 being preferred for coating aluminum to provide protection of the aluminum from plasma. The ""356 patent discloses a ceramic liner of alumina and a ceramic shield of aluminum nitride for the wafer pedestal for use in CVD chambers.
U.S. Pat. No. 5,904,778 discloses a SiC CVD coating on free standing SiC for use as a chamber wall, chamber roof, or collar around the wafer. U.S. Pat. No. 5,292,399 discloses a SiC ring surrounding a wafer pedestal. A technique for preparing sintered SiC is disclosed in U.S. Pat. No. 5,182,059.
In addition to the above, the use of silicon carbide in semiconductor processing equipment is disclosed in U.S. Pat. Nos. 4,401,689 (susceptor tube), 4,518,349 (furnace support rod), 4,999,228 (diffusion tube), 5,074,456 (upper electrode), 5,252,892 (plasma cathode chamber), 5,460,684 (resistive layer of ESC), 5,463,525 (sensing pin), 5,578,129 (filter plate of load lock system), 5,538,230 (wafer boat), 5,595,627 (upper electrode), 5,888,907 (electrode plate), and 5,892,236 (ion implantation device).
Other documents include Japanese Patent Publication Nos. 60-200519 (susceptor), 63-35452 (diffusion oven tube, liner tube, port element, paddle), 63-186874 (microwave heated sample plate), 63-138737 (upper electrode of plasma etch reactor), 3-201322 (coating for part in vacuum environment), and 8-17745 (wafer heater). Of these, Japanese Patent Publication No. 63-35452 discloses parts made of slip cast silicon carbide.
With regard to plasma reactor components such as showerhead gas distribution systems, various proposals have been made with respect to the materials of the showerheads. For instance, commonly owned U.S. Pat. No. 5,569,356 discloses a showerhead of silicon, graphite, or silicon carbide. U.S. Patent No. 5,888,907 discloses a showerhead electrode of amorphous carbon, SiC or Al. U.S. Pat. Nos. 5,006,220 and 5,022,979 disclose a showerhead electrode either made entirely of SiC or a base of carbon coated with SiC deposited by CVD to provide a surface layer of highly pure SiC.
In discussing the need for cleanliness and the elimination of contaminants in the processing of semiconductor wafers, U.S. Pat. No. 5,538,230 references U.S. Pat. Nos. 3,962,391; 4,093,201; 4,203,940; 4,761,134; 4,978,567; 4,987,016 and Japanese Publication No. 50-90184. The ""230 patent also references U.S. Pat. Nos. 3,951,587 and 5,283,089 for discussions of SiC parts and references U.S. Pat. No. 4,761,134 for a discussion of CVD SiC on Si infiltrated SiC or porous Si that has not been filled with Si.
Japanese Publication No. 63-273323 discloses SiC parts for an ECR plasma deposition apparatus wherein silicon dioxide is deposited on samples, the SiC parts being coated with SiC by generating a plasma in the chamber and introducing methane and silane gases into the chamber.
In view of the need for high purity and corrosion resistance for components of semiconductor processing equipment, there is a need in the art for improvements in materials and/or coatings used for such components. Moreover, with regard to the chamber materials, any materials which can increase the service life of a plasma reactor chamber and thus reduce the down time of the apparatus, would be beneficial in reducing the cost of processing the semiconductor wafers.
The invention provides a method of processing semiconductor substrates and reducing particle contamination and/or process drift during consecutive processing of the substrates. The method comprising steps of (a) placing a substrate on a substrate holder in an interior space of a plasma processing chamber, the processing chamber including at lease one slip cast part having a surface exposed to the interior space, the slip cast part having free silicon contained therein and a protective layer on the surface which protects the silicon from being attacked by the plasma in the interior space, (b) processing the substrate by supplying process gas to the processing chamber and energizing the process gas into a plasma state in the processing chamber, the slip cast part being exposed to the plasma and optionally providing a ground path for RF current sustaining the plasma, (c) removing the substrate from the processing chamber, and (d) consecutively processing additional substrates in the processing chamber by repeating steps (a-c) while minimizing particle contamination of the substrates and/or reducing process drift during the processing step as a result of protecting the free silicon from attack by the plasma.
According to one optional aspect of the method, the slip cast part can comprise a liner within a sidewall of the processing chamber and the processing chamber can include a substantially planar antenna which energizes the process gas into the plasma state by supplying RF power to the antenna. For plasma etching of oxide materials, the process gas can comprise one or more hydrofluorocarbon gases. For oxide etching, the plasma preferably comprises a high density plasma which etches an oxide layer on the substrates while an RF bias is applied to the substrates.
The slip cast part can comprise one or more parts of the chamber. For instance, the slip cast part can comprise a liner within a sidewall of the processing chamber, a gas distribution plate supplying the process gas to the processing chamber, a perforated baffle extending between the substrate holder and an inner wall of the processing chamber, a wafer passage insert, a focus ring surrounding the substrate, a tubular liner protecting a process monitoring device, or the like. In a preferred embodiment, the slip cast part is a wafer passage insert fitted in an opening in a ceramic liner within a sidewall of the processing chamber wherein the liner is heated by a heater which maintains the liner at a desired temperature. The slip cast part can consist essentially of silicon impregnated slip cast SiC coated with CVD SiC.
In an exemplary process, a first slip cast part comprises a heated liner and a second slip cast part comprises a plasma screen arranged such that the liner surrounds the substrate holder and the plasma screen extends between the liner and the substrate holder, the liner being heated to a temperature above room temperature during the processing step. In another process, the slip cast part comprises a gas distribution plate having a resistivity high enough to pass RF energy therethrough, the process gas being energized by an antenna which couples RF energy into the chamber through the gas distribution plate. A third slip cast part can comprise a chamber liner having a resistivity below 200 xcexa9xc2x7cm, preferably below 50 xcexa9xc2x7cm, and more preferably below 10 xcexa9xc2x7cm.
The invention also provides a plasma processing system useful for processing semiconductor substrates comprising a plasma processing chamber having an interior space bounded by a chamber sidewall, a substrate support on which a substrate is processed within the interior space arranged such that the chamber sidewall is spaced outwardly of a periphery of the substrate support, a gas supply through which process gas can be supplied to the interior space during processing of the substrate, an energy source which can energize the process gas in the interior space into a plasma state during processing of the substrate, and a slip cast part having a surface thereof exposed to the interior space, the slip cast part having free silicon contained therein and a protective layer on the surface which protects the silicon from being attacked by the plasma in the interior space. According to a preferred embodiment, the slip cast part is of porous silicon carbide backfilled with silicon and the protective layer is a chemical vapor deposited layer of silicon carbide. A preferred slip cast part is a wafer passage insert of a plasma etch reactor wherein the gas supply supplies a fluorocarbon and/or a fluorohydrocarbon to the interior space.
In a less preferred embodiment, the slip cast part is bonded to the chamber by an elastomer joint or the chamber can include a ceramic liner between the chamber sidewall and the substrate support wherein the slip cast part comprises a tubular liner in an opening extending through the liner. A preferred energy source is an antenna such as a planar coil which inductively couples radiofrequency energy through a dielectric member into the chamber.
According to a preferred embodiment, the interior of the chamber is bounded by a showerhead having a silicon carbide surface extending across the top of the chamber, a liner having a silicon carbide surface extending downwardly from the silicon carbide surface of the showerhead, a plasma screen having a silicon carbide surface extending inwardly from the silicon carbide surface of the liner, and the slip cast part comprises a wafer passage insert fitted in an opening in the liner, the CVD SiC coating forming a surface of the wafer passage insert through which a semiconductor wafer passes into and out of the chamber.